What’s the difference?

Principal

Principle

Head, main or most important person

Fundamental truth, law or standard

The principal called the student into his office and explained to him the principle of time management. 

Compliment

Complement

An expression of praise or admiration

Something that contributes to something else and emphasises its quality

He complimented her on her dress, telling her that the colour complemented her eyes. 

Loose

Lose

Not firmly fixed in place, not fitting tightly

Misplace something

If your pants are too loose you might lose them.

Lie

Lay

A horizontal or resting position of a person or animal

Put something down

You lie down on your bed, but you lay a book on a table.

Affect

Effect

Have an effect on, make a difference

A result of an action (noun)
Cause something to happen (verb)

Then

Than

A point in time

Use for comparison

Historic

Historical

Important in history

Something that happened in the past

Partake

Take part

Eat or drink something

Join in an activity, to participate

You take part in the Comrades Marathon and then you partake of food and drink after the race.

Titled

Entitled

Having a title

Having a right to something

In his book titled The advantages of being the boss, the author explains why he thinks people in leadership are entitled to certain privileges.

Defuse

Diffuse

Make a situation less tense or dangerous

Spread something over a wide area or among many people

Stationery

Stationary

Pens, paper, envelopes, and other office supplies

Not moving

Emphasise/emphasize

Empathise/empathize

Stress a word or phrase when speaking

Understand or share the feelings of another

Regards

Regard

Best wishes

View or consider something, in respect of something

Closing greeting in emails:
Kind regards

With regard to (NOT “regards”)

Each other

One another

A reciprocal pronoun between two people

A reciprocal pronoun between more than two people

When you address two people:
Be kind to each other.

When you address a group:
Be kind to one another.

Advice (noun)

Advise (verb)

Guidance, instruction, recommendation

Recommend, counsel, instruct, inform

You advise somebody by giving them advice on something.

Aspire

Inspire

To have hope or ambition to achieve something for oneself

To instil the desire in someone else to achieve something; (also: to breath in)

Wait for

Wait on

“Wait for” something or somebody means waiting for something to happen or somebody to arrive.

“Wait on” somebody means acting as a servant, ie a waiter in restaurant. You can’t “wait on” something.

Definitely

Definitively

Without doubt, certain, for sure

Decisively and with authority, conclusively

Adverse

Averse

Preventing success or development, harmful, unfavourable

Against, having a strong dislike of or opposition to something

Mediator

Intermediary

A mediator assists and guides parties in resolving a conflict. For example, in legal disputes.

An intermediary is a go-between who negotiates an agreement between parties. For example, in buying and selling.

Both are neutral parties acting on behalf of others.